Functional renormalization group approach to SU(N) Heisenberg models: Momentum-space RG for the large-N limit

TL;DR

This paper extends the pseudofermion functional renormalization group method to directly analyze the low-temperature spin liquid phase in SU(N) Heisenberg models, using a momentum-space approach that minimizes bias and improves phase detection.

Contribution

The authors develop a momentum-space pf-FRG approach for large-N SU(N) Heisenberg models, enabling direct study of the spin liquid phase and introducing a new finite temperature regularization scheme.

Findings

Successfully identifies the correct mean-field decoupling channel

Avoids bias from explicit interaction decoupling

Accesses the spin liquid phase with minimal truncation

Abstract

In frustrated magnetism, making a stringent connection between microscopic spin models and macroscopic properties of spin liquids remains an important challenge. A recent step towards this goal has been the development of the pseudofermion functional renormalization group approach (pf-FRG) which, building on a fermionic parton construction, enables the numerical detection of the onset of spin liquid states as temperature is lowered. In this work, focusing on the SU(N) Heisenberg model at large N, we extend this approach in a way that allows us to directly enter the low-temperature spin liquid phase, and to probe its character. Our approach proceeds in momentum space, making it possible to keep the truncation minimalistic, while also avoiding the bias introduced by an explicit decoupling of the fermionic parton interactions into a given channel. We benchmark our findings against exact mean-field results in the large-N limit, and show that even without prior knowledge the pf-FRG approach identifies the correct mean-field decoupling channel. On a technical level, we introduce an alternative finite temperature regularization scheme that is necessitated to access the spin liquid ordered phase. In a companion paper arXiv:1711.02182 we present a different set of modifications of the pf-FRG scheme that allow us to study SU(N) Heisenberg models (using a real-space RG approach) for arbitrary values of N, albeit only up to the phase transition towards spin liquid physics.